Terrestrially transmitted radio broadcast signals of radio broadcasts are transmitted in the frequency ranges of the radio broadcasting bands AM and FM by means of electromagnetic waves whose wavelengths are not shorter than approximately 2 m. New developments with rod-shaped active antennas attached perpendicular to the vehicle body acting as a conducting base surface for the two said broadcasting bands have led to smaller antenna lengths of approximately 20 cm. However, in the construction of vehicles frequently a further reduction in length of such antennas is required.
Due to the narrow construction spaces, the substantial requirement exists with regard to vehicle antennas to minimize their smallness and, in particular to thereafter minimize the outline of the antenna. In particular for satellite radio services as a first radio service the combination of satellite antennas and antennas for other radio services in a narrow space is problematic due to the coupling of radiation between the antennas and the deformation of the directional pattern of the satellite antenna associated therewith. This is, in particular founded on the tightly dimensioned link budget which can lead to a failure of the radio connection due to a drastic deformation of the directional pattern. For example, for satellite antennas in accordance with the standard of satellite radio transmission SDARS in the elevation angular range, e.g. between 25 and/or 30 degrees and 60 and/or 90 degrees an antenna gain of constantly e.g. 2 dBi and/or 3 dBi for circular polarization is strongly required, in dependence on the operator. This requirement exists for an antenna assembled in a center of a planar conductive base plate. This requirement can then only be maintained when the deviation from the ideal radiation characteristic for no spatial angle amounts to more than 0.5 dB. Thus, the directional pattern, in particular in view of the dimension known for antennas of vehicles, has an extremely narrow tolerance. In the DE 101 08 910, e.g. the constructional shape of an antenna is provided which enables the maintenance of the narrowly tolerated directional pattern. With antennas of this type the antenna gain required in the region of the zenith angle can generally be realized without a problem. For this antenna, the reception of terrestrially transmitted signals according to the SDARDS standard are combined with a monopole antenna, whereby a smaller design of the combined antenna advantageous with regard to the use at vehicles results for the first radio service 1. A requirement of narrow tolerance is to be substantially maintained in a corresponding manner for the assembly at a vehicle. Beside this satellite radio broadcast service also further satellite radio services should be possible, such as e.g. the Global Positioning System (GPS).
An antenna according to the state of the art is provided in the DE 101 08 910, it is, however, in no way suitable to receive terrestrially transmitted broadcast signals of radio broadcasts in the frequency ranges of the AM radio bands having free space wavelengths between 600 m and 10 m, as well as the FM radio bands with approximately 3 m free space wavelengths due to its small height.